DRF 3 - Creating Many-to-Many update/create serializer with though table

Question

I am trying to create a reference app in DRF 3 to demonstrate a nested serializer that can create/update models. The sample code below bombs with "*create() argument after ** must be a mapping, not list*" when trying to create the nested models. It is also no clear to me how I'd handle the .update() as in some cases I just want to be establish additional relationships (Persons).

The sample models:

from django.db import models class Person(models.Model):     name = models.CharField(max_length=128) class Group(models.Model):     name = models.CharField(max_length=128)     persons = models.ManyToManyField(Person, through='Membership') class Membership(models.Model):     person = models.ForeignKey(Person)     group = models.ForeignKey(Group) 

And the serializers and viewsets:

from rest_framework.serializers import ModelSerializer from rest_framework.viewsets import ModelViewSet from app.models import Group, Person class PersonSerializer(ModelSerializer):     class Meta:         model = Person class GroupSerializer(ModelSerializer):     persons = PersonSerializer(many=True)     def create(self, validated_data):         persons = validated_data.pop('persons')         group = Group.objects.create(**validated_data)         if persons: # Bombs without this check             Person.objects.create(group=group, **persons)  # Errors here         return group     class Meta:         model = Group  class PersonModelViewSet(ModelViewSet):     serializer_class = PersonSerializer     queryset = Person.objects.all()  class GroupModelViewSet(ModelViewSet):     serializer_class = GroupSerializer     queryset = Group.objects.all() 

I am trying to POST some JSON that inserts a Group with two (related) Persons:

{    "persons": [       { "name" : "name 1" },       { "name" : "name 2" }    ],    "name": "group name 1" } 

Answer 1

I have no clue if there is an easier way, but the only way I managed to get this to work is to reference the 'through' model "memberships" in the Group serializer and write custom code for .create() and .update(). This seems like a lot of work to just set M2M FK's. If someone knows a better way I'd love to hear it.

class GroupMembershipSerializer(ModelSerializer):     class Meta:         model = Membership         fields = ('person',)  class GroupCreateSerializer(ModelSerializer):      memberships = GroupMembershipSerializer(many=True, required=False)      def create(self, validated_data):         person_data = validated_data.pop('memberships')         group = Group.objects.create(**validated_data)         for person in person_data:             d=dict(person)             Membership.objects.create(group=group, person=d['person'])         return group      def update(self, instance, validated_data):         person_data = validated_data.pop('memberships')         for item in validated_data:             if Group._meta.get_field(item):                 setattr(instance, item, validated_data[item])         Membership.objects.filter(group=instance).delete()         for person in person_data:             d=dict(person)             Membership.objects.create(group=instance, person=d['person'])         instance.save()         return instance      class Meta:         model = Group  class GroupCreateModelViewSet(ModelViewSet):     serializer_class = GroupCreateSerializer     queryset = Group.objects.all() 

So you can create a new Group with related Person(s) using:

 {       "name" : "Group 1",       "memberships" : [           { "person" : 1 },          { "person" : 2 }      ]  } 

Answer 2

Use PrimaryKeyRelatedField shown here:

http://www.django-rest-framework.org/api-guide/relations/#primarykeyrelatedfield

class GroupSerializer(serializers.ModelSerializer):     persons = serializers.PrimaryKeyRelatedField(         many=True, queryset=Person.objects.all())      class Meta:         model = Group         fields = ('name', 'persons') 

Create each person first, for example. Person with ID 1, Name = "Bob". Person with ID 2, Name = "Tim". Then post them to the REST Endpoint using their primary keys So:

# Group create() REST endpoint data to POST {'name': 'my group', 'persons': [1, 2]} 

Now the people that you had created prior, are part of that Group.